Block 9 is known to have been mined by Satoshi Nakamoto because Satoshi sent 10BTC from this block to Hal Finney and as far as I remember this is well documented and confirmed by Hal.

This first Bitcoin transaction f4184fc596403b9d638783cf57adfe4c75c605f6356fbc91338530e9831e9e16 spending Satoshi's coins and sending to another person was confirmed in block 170.

The change coins, conveniently transfered to the origin Public Key, were then spent a few blocks later again by Satoshi in a small series of deduction transactions (chronologically from block 9's coinbase -10BTC to Hal Finney, -10BTC, -1BTC, -1BTC and -10BTC, the left change of 18BTC on Public Key 0411db93e1dcdb8a...9b8643f656b412a3 remains unspent 'till today and likely will forever).